Non-selective NMDA receptor antagonists, originally developed in stroke and head trauma, have more recently shown clinical efficacy in treating depression. The non-selective NMDA receptor antagonist, ketamine, has been shown to have rapid onset and efficacy in depression resistant to standard monoamine reuptake inhibitor therapy (Mathews and Zarate, 2013, J. Clin. Psychiatry 74:516-158). However, non-selective NMDA receptor antagonists such as ketamine have a range of undesirable pharmacological activities which limit application in humans. In particular dissociative or psychogenic side effects are particularly prominent for non-selective NMDA receptor antagonists. More recently, NR2B subtype selective NMDA receptor antagonists have demonstrated potential in a wide range of clinical indications. In particular, NR2B antagonists have also demonstrated antidepressant activity in early stage clinical trials (Ibrahim et al., 2012, J. Clin. Psychopharmacol. 32, 551-557; Preskorn et al., 2008, J. Clin. Psychophormacol. 28, 631-637). Furthermore, selective NR2B antagonists have advantages over unselective NMDA receptor antagonists such as ketamine due to greatly diminished dissociative side effects. However, NR2B antagonists described to date have generally exhibited drawbacks with regard to other drug properties which have limited potential use in human drug therapy.